AC3 RF is not Digital Coax?

It all started with the NBA finals. I just wanted to have a better (and hopefully surround sound) for the games. My receiver is a sony 915 (old and not an ES but I love it). Anyway, there is an ac3 rf input, with a coax connector so I figured that it was a regular coax digital input. My cable box has a digital coax output. So I went to JandR and asked the "expert" if coax digital on my cable box was the same as rf ac3. he said yes twice (I had to ask again to double check - I do that). So I bought the coax digital cable, went home, plugged both ends and no sound. I tried to plug my DVD player using its coax output (instead of the cable box) and no sound. So I then checked this forum and found a post saying that ac3 rf is only for LD players. I called OneCall to see if I could find a converter and apparently these guys have never heard of ac3 rf. They told me that it is the same as coax and that sony did not want to pay the royalties to call the input digital coax.

At this point I figured that I would check with some real experts so I'm asking you guys: Is there anything I can do to convert the digital signal from the cable box into ac3 rf to feed my receiver?

I have another solution which is to convert the digital coax into optical but the converter is around $100 and it's just not worth it.

Due to the Database issues, 5 posts in this thread have been deleted including yours so I don't know who you are anymore but I wanted to thank you for the information about parts express. Not sure if I will by the converter to optical (as all my optical inputs are already taken and I would need to buy a switch - and I'm thinking that it's not worth the cost for a few surround programs on cable, plus I'd rather save the $$ for my next receiver ).

Thanks again, parts express is the company I have been looking for for a long time.

Thanks also to everybody who contributed in this discussion and helped me get the answers to my pb.